Two-speed motor



Nov. 13, 1945. E. o. THOMPSON 2,388,884

TWO SPEED MOTOR Filed Oct. 30, 1945 Patented Nov. 13, 1945 TWO-SPEED MOTOR Elmer 0. Thompson, Grasmere, N; Y., assignor to Philco Radio and Television Corporation, Philadelphia, Pa., a corporation of Delaware Application October 30, 1943, Serial No. 508,282

,6 Claims.

This invention relates to electric motors and has for its main object to provide a. dual-speed, single-phase alternating current machine which is dependable and possessed of good operating characteristics and yet is susceptible of being manufactured very cheaply.

More specifically, the object is to provide a low cost, dual-speed fractional horse-power motor which is suitable for operating phonograph recorders and reproducers.

The standard turntable speedier commercial phonograph disc recording i 78 R. P. M. and, with a few possible exceptions, all outstanding home recorders and reproducers are designed to operate only at that speed. However, by using somewhat larger discs, it is feasible to record at much lower speeds and thus greatly increase the playing time per unit of record cost without detracting from the quality. Furthermore, as respects the kind of material most commonly inscribed on home recordings, it makes out little difference whether or not the higher frequencies are excessively attenuated; and it is believed that the majority of people who use home recorders and small discs would prefer to sacrifice the higher frequencies in favor of increased playing time-especially when the recording is speech and not music.

In order to play standard recordings, it is, of course, essential that a reproducer operate at a turntable speed of 78 R. P. M; and ii the same machine is to be adapted for recording and reproducing at slow speed, it obviously i necessary to provide for two-speed operation. This can readily be done through the agency of a speedchanging gear or through the employment of high and low speed motors or a dual-speed motor; and

no major problem is involved so long as the machine is intended to sell at a price which permits oi. the use of comparatively costly component parts. But a very substantial if not major part of the market for home recorders and reproducers lies in the extreme low-price field, and it has been found that the costs of satisfactory speed-changing gears and, likewise, thosev of suitable dualspeed motors, such as have heretofore been available, are too high to permit of incorporation in the cheapest machines. Yet no reputable manuiacturer can aflord to attach his name to a product, no matter how cheap, which will not stand up and give satisfaction. 7

The prior art affords many excellent dualspeed alternating current motors which would he perfectly satisfactory operationally; but so far as is known there is no prior motor of that character which is both acceptable from the performance standpoint and capable of being manulectured at a cost low enough to permit of incorporation in very low-priced phonographs.

The problem which this situation presented was a difiicult one, in view of the very low permissible manufacturing cost, but it has been solved by the present invention which is based on the discovery that it i possible to utilize, in combination, the known principle of the shaded pole motor and the known principle of the capacitor type motor and thereby achieve a dual-speed motor which, with the necessary external controls, is but little more costly than the cheapest of single-speed induction motors.

A feature of the invention is that it enables the employment of concentrated, pole-pieces, each with a single preformed winding which can be quickly put in, place, together with a single turn shading coil consisting of a copper loop which likewise is quickly applicable to the shaded poles. Another feature is that all of the main windmgs are used for both high and low speed-it being unnecessary to provide separate high and low speed windings.

Still another feature is that the shading coils, which are provided primarily for low-speed operation, aid rather than hinder the high speed operation of the motor. I

The preferred embodiment of this invention is illustrated in the accompanying drawing, where- Fig. 1 shows, somewhat diagrammatically, a dual-speed induction motor with external circuit connections including 9, speed-changing switch and electrostatic capacitor;

Fig. 2 is a schematic diagram showing the manner in which the stator coils and capacitor are interconnected, and, in turn, connected to the power-supply feed line to bring about high-speed operation; and

Fig. 3 is a schematic diagram showing the manner in which the stator coils are interconnected, and, in turn, connected to the power-supp1y feed line to bring about low-speed operation.

The motor per se, shown in Fig. 1, comprises a stator frame 3 having four concentrated polepieces 2, 3, 4 and 5 spaced degrees apart and including a conventional squirrel cage rotor 6. Each of said pole-pieces is slotted to accommodate a shading coil, which may be a single loop of copper slipped into place and secured irictionally. By reason of the shading coils the mag netic flux in pole portions 211, 3c, ta and 6a is caused to lag behind the flux through the main portionsoi the pole-piece and, hence, said oleportions' 2a5a constitute auxiliary poles, or socalled shaded poles, which are so spacedwith rewindings or principal coils. These principal coils 10 the scope of the appended claims are also to be are preferably machine wound and pre-formed so that they can easily be slipped onto the polepieces; and they require no attachment other than their frictional adherence to the pole-pieces. Obviously, the job of assembling the motor is exceedingly simple; and the component parts are equally simple and cheap, as will be self-evident. Moreover, since all four principal coils may be identical, there is no time lost in ascertainin that the right coil is applied to each pole-piece.

Two leads from each principal coil are brought out through one or more suitable openings in the motor frame and these may conveniently be identified by means of colored clips.

A switch l2, shown diagrammatically in Fig. 1, is mounted outside the motor at any convenient point, as is also a capacitor it.

The connections between the motor, switch i2 and capacitor I3 are such that when the switch is in one of its two positions the motor is conditioned for high speed operation, whereas throwing of the switch to its alternate positionso changes the connections as to bring about low speed operation. The wiring is fully illustrated in Fig. l and needs no detailed explanation aside from mentioning that L1 and L2 are the two wires of the feed line.

Switch l2 has four blade Hi, l5, l6 and H which, in the upper position marked Ln 8., establish the several connections for low speed operation, and in the lowerposition, marked S., establish the alternate connections for high speed operation.

Fig. 2 shows in simplified form the circuit arrangement for high speed operation while Fig. 3 shows the circuit arrangement for low speed operation.

It will be noted that principal coils 8, 9, l and l l are used for both speeds. This is an important consideration since it means that an irreducible minimum number of windings are required.

The high speed connections of Fig. 2 correspond to those of the familiar single-speed capacitor type motor wherein principal coils 9 and II constitute what are usually termed the main windings, while principal coils 8 and I0 constitute what are usually termed the auxiliary windings. These latter coils are in series with capacitor l3. By virtue of the latter, the current is caused to lag in the auxiliary windings, and i this serves to engender the necessary rotating field. The relative polarities are indicated in Fig. 2, from which it will be apparent that the motor is of the two-pole variety when thus connected. It is to be understood that due to the phase difierence between the currents flowing inmounting near the turntable. In one physical embodiment of the invention comprising a motor structure of conventional phonograph size, the capacitor l3 had a capacity of about 2 microfarads.

While only a four-pole motor has been shown and described, it will be self-evident that the number of poles can be multiplied to any desired extent. Such other modifications as fall within deemed within the scope of the invention.

I claim:

l. A dual-speed, single-phase induction motor and control system therefor comprising, in com- 5 bination: a rotor, four field pole-pieces spaced in quadrature about said rotor, each of said polepieces including a main pole portion and a shaded pole portion, four principal windings, each wound on one of said pole-pieces individually, four shading coils, each wound on one of said shaded pole portions individually, a pair of feed-line terminals, a two-way switch having a high-speed position and a low-speed position, an electrostatic capacitor and leads interconnecting said principal windings with said switch and said feed line rent flow in one pair of oppositely situated principal windings is substantially phase-displaced with respect to the current fiow in the other pair of principal windings, said interconnections also being such, when said switch is in its low-speed 40 position, that the current in all said principal windings is in phase,'and adjacent main poles are of opposite magnetic polarity.

2. A dual-speed, single-phase induction motor and'control system therefor comprising, in combination: a rotor, four field pole-pieces spaced in quadrature about said rotor, each of said polepieces including a main pole portion and a shaded pole portion, four principal windings, each wound on one of said pole-pieces individually, four. shading coils, .each wound on one of.said shaded poles individually, a pair of feed-line terminals, a twoway switch having a high-speed position and a low-speed position, a non-inductive impedance, and leads interconnecting said principal windings with said switch and said feedline terminals, the

interconnections being such, when said switch is in its high-speed position, that said impedance is connected in series with one pair only of oppositely situated principal windings, and all of said principal windings are so connected to said feed-line terminals that the pole faces at diametrically opposite -sides of said rotor are of magnetically, opposite polarity, said impedance being of such magnitude that the'current fiow in 5 one pair of oppositely situated principal windings is substantially phase displaced with respect to the current fiow in the other pair of principal windings, said interconnections also being such, when said switch is in its low-speed position, that the current in all said principal windings is in phase, and adjacent main poles are of opposite magnetic polarity.

3. In combination, an induction-motor comprising a rotor, a, stator including at least two pairs of poles, the poles of each pair being oppositely situated and each pole having a main pole portion and a shaded pole portion, similar principal windings on said main pole portions and similar shading coils on said shaded pole portions, it non-inductive impedance, means operable at will to interconnectsaid principal windings and said impedance so as to condition said motor for operation at one speed, and means operable at will to interconnect said principal windings exclusive of said impedance so as to condition said motor for operation at a diiferent speed.

4. In combination, an induction motor comprising a rotor, a stator including two pairs of poles, the poles of each pair being oppositely situated and each pole having a main pole portion and a, shaded pole portion, similar principal windings on said main pole portions and similar shading coils on said shaded pole portions, a capacitor, means operable at will to interconnect said principal windings and said capacitor so that each opposed pair of windings are serially connected in such fashion that the opposed poles are 01' opposite magnetic polarity, and said capacitor is connected in series with one pair of windings, whereby the motor is connected as a two-pole motor and operates at a predetermined high speed, and means operable at will to reverse the connections of two adjacent windings and to remove said capacitor from the motor circuit,

' eluding a main pole portion and a shaded pole motor comprising a. rotor, a stator including plural pairs of oppositely situated poles arranged about said rotor, field windings on the respective poles, a pair of feed-line terminals, a capacitor, means operable at will to interconnect said windings and said capacitor so that the windings on portion, four principal windings, each wound on one of said pole-pieces individually, four shading coils, each wound on one of said shaded pole portions individually, a pair of feed-line terminals, a two-way switch having a high-speed position and a low-speed position, an electrostatic capacitor and leads interconnecting said principal windings with said switch and said feed-line terminals, the interconnections being such, when said switch is in its high-speed position, that the principal windings on opposed pole-pieces are connected in series with each other and the serles connected windings are connected in parallel to the feed-line terminals with said capacitor connected in series with one pair only of oppositely situated series windings, so that the main pole faces at diametrically opposite sides of said rotor are of magnetically opposite polarity, said capacitor being of such magnitude that the current flow in one pair of oppositely situated principal windings is substantially phase-displaced with respect to the current flow in the other pair of principal windings, said interconnections also being such, when said switch is in its low-speed position, that the principal windings on opposite pole-pieces are series connected with each other andthe series connected windings are connected in parallel with said feed-line terminals with the current in all said principal windings in phase, and with adjacent main poles being of opposite magnetic polarity and with said capacitor open clrcuited with respect to all said windings.

m o. THOMPSON. 

